1. Field of the Invention
The present invention relates to a lubricant-tight vane rotary vacuum pump that includes at least one pump stage having a pump stage housing, a safety valve for controlling gas flow to the pump stage housing, a lubricant pump having an inlet and an outlet, a lubricant reservoir at least partially surrounding the pump stage housing, and a hydraulic conduit connecting the lubricant pump outlet with the safety valve, with a pressurized lubricant flow through the hydraulic conduit opening the safety valve.
2. Description of the Prior Art
A vane rotary vacuum pump of the type described above is disclosed in German Publication DE-OS 10 204 024 554 in which the lubricant, among others, is used for opening a hydraulically operated safety valve. The safety valve opens as soon as a lubricant pump, which is driven by the pump shaft, pressurizes the lubricant fed to the safety valve.
The lubricant also serves for lubricating the vanes which are arranged in the compression chamber of the vacuum pump and the rotation of which produces a pumping effect. Simultaneously, the lubricant seals the gaps between the vanes, the shaft and the compression chamber housing. This housing, which forms the pump stage housing, is submerged in a lubricant reservoir and is, therefore, surrounded by the lubricant over a major portion of its periphery. The heat, which is generated within the pump stage housing, is transmitted to the lubricant surrounding the housing.
The problem with this type of vacuum pumps consists in that the lubricant is heated progressively, whereby its chemical structure changes.
Accordingly, an object of the invention is to provide a vane rotary vacuum pump in which overheating of the lubricant is prevented.